Here's an update on how I got Tomcat to run on my mac. First I downloaded all the recent stuff (which may or may not be a requirement); so, I installed XCode Tools 1.5 and then Java 1.4.2 Update 1 Developer Tools.
Then I went to the directory /Library/Tomcat/bin
and issued this command:
sh -v startup.sh
Then I went to my Safari browser and placed in this URL:
The only thing which fooled me was that I always thought that the default port for Tomcat was 8080, and that may have been why I could not get Tomcat to function.
Finally, I did make one other change though I cannot say that it is critical for Tomcat alone or if it is critical only if you use JBoss: it was a writeup at apple about what happens after you install JRE 1.4 and how you need to change a line within a JBOSS file, but I don't have the particulars.
I've not tried the version of Tomcat delivered with the developer tools CD, but perhaps they switched the default port to stop it clashing with something (JBoss, perhaps?). Speaking of JBoss, I seem to remember having to change the /Library/JBoss/3.2/bin/run.conf file when Java 1.4.2 was installed via the software update mechanism. I think it's the line starting JAVA=, but the full version of my file is as follows.